'Reliability' of any research is the degree to which it gives an accurate score across a range of measurement. It can thus be viewed as being 'repeatability' or 'consistency'. In summary:

Inter-rater: Different people, same test.
Test-retest: Same people, different times.
Parallel-forms: Different people, same time, different test.
Internal consistency: Different questions, same construct.
Inter-Rater Reliability
When multiple people are giving assessments of some kind or are the subjects of some test, then similar people should lead to the same resulting scores. It can be used to calibrate people, for example those being used as observers in an experiment.

TYPES OF VALIDITY
Here is an overview on the main types of validity used for the scientific method.
by Experiment-Resources.com (2009)
http://www.experiment-resources.com/types-of-validity.html

"Any research can be affected by different kinds of factors which, while extraneous to the concerns of the research, can invalidate the findings" (Seliger & Shohamy 1989, 95).

Let's take a look on the the most frequent uses of validity in the scientific method:

EXTERNAL VALIDITY
External validity is about generalization: To what extent can an effect in research, be generalized to populations, settings, treatment variables, and measurement variables?
External validity is usually split into two distinct types, population validity and ecological validity and they are both essential elements in judging the strength of an experimental design.

INTERNAL VALIDITY
Internal validity is a measure which ensures that a researcher's experiment design closely follows the principle of cause and effect.

"Could there be an alternative cause, or causes, that explain my observations and results?"

TEST VALIDITY
Test validity is an indicator of how much meaning can be placed upon a set of test results.